Conventionally, in a case of detecting an extremely minute substance, various sample detection apparatuses capable of detecting such a substance by applying a physical phenomenon of the substance have been used.
One of such sample detection apparatuses is a surface plasmon resonance apparatus (hereinafter, referred to as “SPR apparatus”), for example, for detecting an extremely minute analyte in a living body by applying a phenomenon (surface plasmon resonance (SPR) phenomenon) that obtains a high light output by resonance of electrons and light in a fine region at a nanometer level or the like.
In addition, a surface plasmon-field enhanced fluorescence spectroscopic apparatus (hereinafter, referred to as “SPFS apparatus”) capable of detecting an analyte with higher accuracy than the SPR apparatus based on principle of surface plasmon-field enhanced fluorescence spectroscopy (SPFS) applying a surface plasmon resonance (SPR) phenomenon is also one of such sample detection apparatuses.
This surface plasmon-field enhanced fluorescence spectroscopy (SPFS) obtains an effect of enhancing an electric field of surface plasmon light by generating surface plasmon light (compressional wave) on a surface of a metal film under a condition that excitation light such as laser light emitted from a light source undergoes attenuated total reflectance (ATR) on the surface of the metal film to increase the amount of photons possessed by the excitation light emitted from the light source by dozens of times to several hundreds of times.
FIG. 13 is a schematic configuration diagram for explaining a configuration of a conventional SPFS system.
A conventional SPFS system 100 includes a sensor chip 114 including a prism-shaped dielectric member 102 having a substantially trapezoidal vertical cross section, a metal film 104 formed on a horizontal upper surface 102a of the dielectric member 102, a reaction layer 106 formed on an upper surface of the metal film 104, and a channel forming member 110 and a channel lid member 112 forming a channel 108 so as to surround the reaction layer 106. The sensor chip 114 is loaded in a sensor chip loading portion 116 of an SPFS apparatus 101.
The reaction layer 106 of the sensor chip 114 has a solid phase film for capturing an analyte labeled with a fluorescent substance. By feeding a sample liquid containing the analyte to the channel 108, the analyte can be fixed onto the metal film 104.
In addition, a light receiving unit 120 of the SPFS apparatus 101 is disposed above the sensor chip 114 in order to measure the intensity of fluorescence 118 emitted by a fluorescent substance excited by surface plasmon light (compressional wave) generated on the metal film 104.
In addition, as illustrated in FIG. 13, a light source 122 of the SPFS apparatus 101 is disposed on one side surface (incidence surface 102b) side below the dielectric member 102. Excitation light 124 emitted from the light source 122 is incident on an incidence surface 102b of the dielectric member 102 from a lower portion of an outside of the dielectric member 102. The metal film 104 formed on the upper surface 102a of the dielectric member 102 is irradiated with the excitation light 124 through the dielectric member 102.
In the conventional SPFS system 100 configured as described above, by emitting the excitation light 124 from the light source 122 toward the metal film 104, surface plasmon light (compressional wave) is generated on a surface of the metal film 104. This surface plasmon light (compressional wave) excites a fluorescent substance labelling an analyte, and the fluorescence 118 is emitted. The fluorescence 118 is detected by the light receiving unit 120, and the amount of analyte is calculated based on the light amount of the fluorescence 118.
In such SPFS measurement, the light amount of the fluorescence 118 is lower than the excitation light amount by about ten digits. Therefore, even if a small amount of the excitation light 124 is incident on the light receiving unit 120, an S/N ratio deteriorates, and detection accuracy deteriorates. Therefore, it is important to reduce stray light.
As illustrated in FIG. 13, the excitation light 124 is incident from the incidence surface 102b of the dielectric member 102, is then reflected by the metal film 104, and is emitted from an emission surface 102c of the dielectric member 102.
However, as illustrated in FIG. 13, a part of the excitation light 124 is reflected by the emission surface 102c of the dielectric member 102, and there is emission surface reflected light 124b emitted from the incidence surface 102b of the dielectric member 102.
As illustrated in FIG. 13, when the emission surface reflected light 124b is incident on the channel lid member 112, the emission surface reflected light 124b becomes light guided in the channel lid member 112. If the emission surface reflected light 124b exists in a visual field range of the light receiving unit 120, autofluorescence in the channel lid member 112 is detected, leading to deterioration of an S/N ratio.
Incidentally, the emission surface reflected light 124b usually has a light amount of about 4% of the excitation light 124, and this amount is sufficiently large with respect to the fluorescence 118. Therefore, the emission surface reflected light 124b can be said to be stray light to be removed.
In order to remove such stray light, in Patent Literature 1, as illustrated in FIG. 14, a light absorbing portion 126 for absorbing metal film reflected light reflected by the metal film 104 is disposed in an optical path of the dielectric member 102.
In addition, in Patent Literature 2, as illustrated in FIG. 15, by disposing an excitation light cut filter (wavelength filter) 128 for removing scattered light and reflected light in the sensor chip 114 on an upper surface of the sensor chip 114, the excitation light 124 is cut.